Macros
#define	_DEFAULT_SOURCE
	strcasecmp() feature macro starting glibc 2.20 (2014-09-08)

Functions
double	get_ut1_to_tt (int leap_seconds, double dut1)

double	get_utc_to_tt (int leap_seconds)

double	novas_date (const char *restrict date)

double	novas_date_scale (const char restrict date, enum novas_timescale restrict scale)

double	novas_diff_tcb (const novas_timespec t1, const novas_timespec t2)

double	novas_diff_tcg (const novas_timespec t1, const novas_timespec t2)

double	novas_diff_time (const novas_timespec t1, const novas_timespec t2)

double	novas_get_split_time (const novas_timespec restrict time, enum novas_timescale timescale, long restrict ijd)

double	novas_get_time (const novas_timespec *restrict time, enum novas_timescale timescale)

time_t	novas_get_unix_time (const novas_timespec restrict time, long restrict nanos)

int	novas_iso_timestamp (const novas_timespec restrict time, char restrict dst, int maxlen)

int	novas_offset_time (const novas_timespec time, double seconds, novas_timespec out)

double	novas_parse_date (const char restrict date, char *restrict tail)

double	novas_parse_date_format (enum novas_calendar_type calendar, enum novas_date_format format, const char restrict date, char *restrict tail)

enum novas_timescale	novas_parse_timescale (const char restrict str, char *restrict tail)

int	novas_print_timescale (enum novas_timescale scale, char *restrict buf)

int	novas_set_split_time (enum novas_timescale timescale, long ijd, double fjd, int leap, double dut1, novas_timespec *restrict time)

int	novas_set_time (enum novas_timescale timescale, double jd, int leap, double dut1, novas_timespec *restrict time)

int	novas_set_unix_time (time_t unix_time, long nanos, int leap, double dut1, novas_timespec *restrict time)

enum novas_timescale	novas_timescale_for_string (const char *restrict str)

int	novas_timestamp (const novas_timespec restrict time, enum novas_timescale scale, char restrict dst, int maxlen)

int	tdb2tt (double jd_tdb, double restrict jd_tt, double restrict secdiff)

double	tt2tdb (double jd_tt)

Detailed Description

Date: Created on Jun 24, 2024

Author: Attila Kovacs

Since: 1.1

A set of SuperNOVAS routines to make handling of astronomical timescales and conversions among them easier.

See also: frames.c

Function Documentation

◆ get_ut1_to_tt()

double get_ut1_to_tt	(	int	leap_seconds,
		double	dut1
	)

Returns the TT - UT1 time difference given the leap seconds and the actual UT1 - UTC time difference as measured and published by IERS.

NOTES:

The current UT1 - UTC time difference, and polar offsets, historical data and near-term projections are published in the <a href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html>IERS Bulletins

Parameters

leap_seconds	[s] Leap seconds at the time of observations
dut1	[s] UT1 - UTC time difference [-0.5:0.5]

Returns: [s] The TT - UT1 time difference that is suitable for used with all calls in this library that require a ut1_to_tt argument.

See also: get_utc_to_tt(); place(); cel_pole()

Since: 1.0

Author: Attila Kovacs

References get_utc_to_tt().

◆ get_utc_to_tt()

double get_utc_to_tt ( int leap_seconds )

Returns the difference between Terrestrial Time (TT) and Universal Coordinated Time (UTC)

Parameters

leap_seconds [s] The current leap seconds (see IERS Bulletins)

Returns: [s] The TT - UTC time difference

See also: get_ut1_to_tt(); julian_date()

Since: 1.0

Author: Attila Kovacs

References NOVAS_TAI_TO_TT.

◆ novas_date()

double novas_date ( const char *restrict date )

Returns a Julian date (in non-specific timescale) corresponding the specified input string date/time. E.g. for "2025-02-28T09:41:12.041+0200", with some flexibility on how the date is represented as long as it's YMD date followed by HMS time. For other date formats (MDY or DMY) you can use novas_parse_date_format() instead.

Parameters

date	The date specification, possibly including time and timezone, in a standard format. See novas_parse_date() on more information on acceptable date/time formats.

Returns: [day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since: 1.3

Author: Attila Kovacs

See also: novas_date_scale(); novas_parse_date(); novas_parse_date_format(); novas_iso_timestamp()

References novas_parse_date().

◆ novas_date_scale()

double novas_date_scale	(	const char *restrict	date,
		enum novas_timescale *restrict	scale
	)

Returns a Julian date and the timescale corresponding the specified input string date/time and timescale marker. E.g. for "2025-02-28T09:41:12.041+0200 TAI", with some flexibility on how the date is represented as long as it's YMD date followed by HMS time. For other date formats (MDY or DMY) you can use novas_parse_date_format() instead.

Parameters

	date	The date specification, possibly including time and timezone, in a standard format. See novas_parse_date() on more information on acceptable date/time formats.
[out]	scale	The timescale constant, or else -1 if the string could not be parsed into a date and timescale. If the string is a bare timestamp without an hint of a timescale marker, then NOVAS_UTC will be assumed.

Returns: [day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since: 1.3

Author: Attila Kovacs

See also: novas_date(); novas_timestamp()

References novas_parse_date(), and novas_parse_timescale().

◆ novas_diff_tcb()

double novas_diff_tcb	(	const novas_timespec *	t1,
		const novas_timespec *	t2
	)

Returns the Barycentric Coordinate Time (TCB) based time difference (t1 - t2) in days between two astronomical time specifications. TCB progresses slightly faster than time on Earth, at a rate about 1.6&times10^-8 higher, due to the lack of gravitational time dilation by the Earth or Sun.

Parameters

t1	First time
t2	Second time

Returns: [s] Precise TCB time difference (t1-t2), or NAN if one of the inputs was NULL (errno will be set to EINVAL)

See also: novas_diff_tcg(); novas_diff_time()

Since: 1.1

Author: Attila Kovacs

References novas_diff_time().

◆ novas_diff_tcg()

double novas_diff_tcg	(	const novas_timespec *	t1,
		const novas_timespec *	t2
	)

Returns the Geocentric Coordinate Time (TCG) based time difference (t1 - t2) in days between two astronomical time specifications. TCG progresses slightly faster than time on Earth, at a rate about 7&times10^-10 higher, due to the lack of gravitational time dilation by Earth. TCG is an appropriate time measure for a spacecraft that is in the proximity of the orbit of Earth, but far enough from Earth such that the relativistic effects of Earth's gravity can be ignored.

Parameters

t1	First time
t2	Second time

Returns: [s] Precise TCG time difference (t1-t2), or NAN if one of the inputs was NULL (errno will be set to EINVAL)

See also: novas_diff_tcb(); novas_diff_time()

Since: 1.1

Author: Attila Kovacs

References novas_diff_time().

◆ novas_diff_time()

double novas_diff_time	(	const novas_timespec *	t1,
		const novas_timespec *	t2
	)

Returns the Terrestrial Time (TT) based time difference (t1 - t2) in days between two astronomical time specifications.

Parameters

t1	First time
t2	Second time

Returns: [s] Precise time difference (t1-t2), or NAN if one of the inputs was NULL (errno will be set to EINVAL)

See also: novas_set_time(); novas_offset_time(); novas_diff_tcb(); novas_diff_tcg()

Since: 1.1

Author: Attila Kovacs

References novas_timespec::fjd_tt, and novas_timespec::ijd_tt.

◆ novas_get_split_time()

double novas_get_split_time	(	const novas_timespec *restrict	time,
		enum novas_timescale	timescale,
		long *restrict	ijd
	)

Returns the fractional Julian date of an astronomical time in the specified timescale, as an integer and fractional part. The two-component split of the time allows for absolute precisions at the picosecond level, as opposed to novas_set_time(), whose precision is limited to a few microseconds typically.

The accuracy of Barycentric Time measures (TDB and TCB) relative to other time measures is limited by the precision of the tbd2tt() implemenation, to around 10 μs.

REFERENCES:

IAU 1991, RECOMMENDATION III. XXIst General Assembly of the International Astronomical Union. Retrieved 6 June 2019.
IAU 2006 resolution 3, see Recommendation and footnotes, note 3.
Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
Kaplan, G. (2005), US Naval Observatory Circular 179.
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

	time	Pointer to the astronomical time specification data structure.
	timescale	The astronomical time scale in which the returned Julian Date is to be provided
[out]	ijd	[day] The integer part of the Julian date in the requested timescale. It may be NULL if not required.

Returns: [day] The fractional part of the Julian date in the requested timescale or NAN is the time argument is NULL (ijd will be set to -1 also).

See also: novas_set_split_time(); novas_get_time()

Since: 1.1

Author: Attila Kovacs

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

◆ novas_get_time()

double novas_get_time	(	const novas_timespec *restrict	time,
		enum novas_timescale	timescale
	)

Returns the fractional Julian date of an astronomical time in the specified timescale. The returned time is accurate to a few μs (microsecond) due to the inherent precision of the double-precision result. For higher precision applications you may use novas_get_split_time() instead, which has an inherent accuracy at the picosecond level.

Parameters

time	Pointer to the astronomical time specification data structure.
timescale	The astronomical time scale in which the returned Julian Date is to be provided

Returns: [day] The Julian date in the requested timescale.

See also: novas_set_time(); novas_get_split_time()

Since: 1.1

Author: Attila Kovacs

References novas_get_split_time().

◆ novas_get_unix_time()

time_t novas_get_unix_time	(	const novas_timespec *restrict	time,
		long *restrict	nanos
	)

Returns the UNIX time for an astronomical time instant.

Parameters

	time	Pointer to the astronomical time specification data structure.
[out]	nanos	[ns] UTC sub-second component. It may be NULL if not required.

Returns: [s] The integer UNIX time, or -1 if the input time is NULL.

See also: novas_set_unix_time(); novas_get_time()

Since: 1.1

Author: Attila Kovacs

References novas_get_split_time(), and NOVAS_UTC.

◆ novas_iso_timestamp()

int novas_iso_timestamp	(	const novas_timespec *restrict	time,
		char *restrict	dst,
		int	maxlen
	)

Prints a UTC-based ISO timestamp to millisecond precision to the specified string buffer. E.g.:

 2025-01-26T21:32:49.701Z

NOTES:

The timestamp uses the conventional date of the time. That is Gregorian dates after the Gregorian calendar reform of 15 October 1582, and Julian/Roman dates prior to that.
B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

	time	Pointer to the astronomical time specification data structure.
[out]	dst	Output string buffer. At least 25 bytes are required for a complete timestamp with termination.
	maxlen	The maximum number of characters that can be printed into the output buffer, including the string termination. If the full ISO timestamp is longer than `maxlen`, then it will be truncated to fit in the allotted space, including a termination character.

Returns: the number of characters printed into the string buffer, not including the termination. As such it is at most maxlen - 1.

Since: 1.3

Author: Attila Kovacs

See also: novas_timestamp(); novas_parse_time()

References novas_get_split_time(), and NOVAS_UTC.

◆ novas_offset_time()

int novas_offset_time	(	const novas_timespec *	time,
		double	seconds,
		novas_timespec *	out
	)

Increments the astrometric time by a given amount.

Parameters

	time	Original time specification
	seconds	[s] Seconds to add to the original
[out]	out	New incremented time specification. It may be the same as the input.

Returns: 0 if successful, or else -1 if either the input or the output is NULL (errno will be set to EINVAL).

See also: novas_set_time(); novas_diff_time()

Since: 1.1

Author: Attila Kovacs

References novas_timespec::fjd_tt, and novas_timespec::ijd_tt.

◆ novas_parse_date()

double novas_parse_date	(	const char *restrict	date,
		char **restrict	tail
	)

Parses a date/time string into a Julian date specification. Typically the date may be an ISO date specification, but with some added flexibility. The date must be YMD-type with full year, followed the month (numerical or name or 3-letter abbreviation), and the day. The components may be separated by dash -, underscore _, dot ., slash '/', or spaces/tabs, or any combination thereof. The date may be followed by a time specification in HMS format, separated from the date by the letter T or t, or spaces, comma ,, or semicolon ;, or underscore _ or a combination thereof. Finally, the time may be followed by the letter Z, or z (for UTC) or else {+/-}HH[:[MM]] time zone specification.

For example:

 2025-01-26
 2025 January 26
 2025_Jan_26
 2025-01-26T19:33:08Z
 2025.01.26T19:33:08
 2025 1 26 19h33m28.113
 2025/1/26 19:33:28+02
 2025-01-26T19:33:28-0600
 2025 Jan 26 19:33:28+05:30

are all valid dates that can be parsed.

NOTES:

This function uses Gregorian dates since their introduction on 1582 October 15, and Julian/Roman datew before that, as was the convention of the time. I.e., the day before of the introduction of the Gregorian calendar reform is 1582 October 4.
B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

	date	The date specification, possibly including time and timezone, in a standard format.
[out]	tail	(optional) If not NULL it will be set to the next character in the string after the parsed time.

Returns: [day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since: 1.3

Author: Attila Kovacs

See also: novas_date(); novas_date_scale(); novas_parse_date_format(); novas_timescale_for_string(); novas_iso_timestamp(); novas_timestamp()

References NOVAS_ASTRONOMICAL_CALENDAR, novas_parse_date_format(), and NOVAS_YMD.

◆ novas_parse_date_format()

double novas_parse_date_format	(	enum novas_calendar_type	calendar,
		enum novas_date_format	format,
		const char *restrict	date,
		char **restrict	tail
	)

Parses a calndar date/time string, expressed in the specified type of calendar, into a Julian day (JD). The date must be composed of a full year (e.g. 2025), a month (numerical or name or 3-letter abbreviation, e.g. "01", "1", "January", or "Jan"), and a day (e.g. "08" or "8"). The components may be separated by dash -, underscore _, dot ., slash '/', or spaces/tabs, or any combination thereof. The components will be parsed in the specified order.

The date may be followed by a time specification in HMS format, separated from the date by the letter T or t, or spaces, comma ,, or semicolon ; or underscore '_', or a combination thereof. Finally, the time may be followed by the letter Z, or z (for UTC) or else by a {+/-}HH[:[MM]] time zone specification.

For example, for format NOVAS_YMD, all of the following strings may specify the date:

 2025-01-26
 2025 January 26
 2025_Jan_26
 2025-01-26T19:33:08Z
 2025.01.26T19:33:08
 2025 1 26 19h33m28.113
 2025/1/26 19:33:28+02
 2025-01-26T19:33:28-0600
 2025 Jan 26 19:33:28+05:30

are all valid dates that can be parsed.

If your date format cannot be parsed with this function, you may parse it with your own function into year, month, day, and decimal hour-of-day components, and use julian_date() with those.

NOTES:

B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

	calendar	The type of calendar to use: NOVAS_ASTRONOMICAL_CALENDAR, NOVAS_GREGORIAN_CALENDAR, or NOVAS_ROMAN_CALENDAR.
	format	Expected order of date components: NOVAS_YMD, NOVAS_DMY, or NOVAS_MDY.
	date	The date specification, possibly including time and timezone, in the specified standard format.
[out]	tail	(optional) If not NULL it will be set to the next character in the string after the parsed time.

Returns: [day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since: 1.3

Author: Attila Kovacs

See also: novas_parse_date(); novas_timescale_for_string(); novas_iso_timestamp(); julian_date()

References novas_debug(), NOVAS_DEBUG_OFF, NOVAS_DMY, novas_get_debug_mode(), novas_jd_from_date(), NOVAS_MDY, novas_parse_hms(), and NOVAS_YMD.

◆ novas_parse_timescale()

enum novas_timescale novas_parse_timescale	(	const char *restrict	str,
		char **restrict	tail
	)

Parses the timescale from a string containing a standard abbreviation (case insensitive), and returns the updated parse position after the timescale specification (if any). The following timescale values are recognised: "UTC", "UT", "UT0", "UT1", "GMT", "TAI", "GPS", "TT", "ET", "TCG", "TCB", "TDB".

Parameters

	str	String specifying an astronomical timescale. Leading white spaces will be skipped over.
[out]	tail	(optional) If not NULL it will be set to the next character in the string after the parsed timescale specification.

Returns: The SuperNOVAS timescale constant (<=0), or else -1 if the string was NULL, empty, or could not be matched to a timescale value (errno will be set to EINVAL also).

Since: 1.3

Author: Attila Kovacs

See also: novas_timescale_for_string(); novas_set_time(); novas_set_split_time(); novas_print_timescale()

References novas_timescale_for_string(), and NOVAS_UTC.

◆ novas_print_timescale()

int novas_print_timescale	(	enum novas_timescale	scale,
		char *restrict	buf
	)

Prints the standard string representation of the timescale to the specified buffer. The string is terminated after. E.g. "UTC", or "TAI". It will print dates in the Gregorian calendar, which was introduced in was introduced on 15 October 1582 only. Thus the

Parameters

scale	The timescale
buf	String in which to print. It should have at least 4-bytes of available storage.

Returns: the number of characters printed, not including termination, or else -1 if the timescale is invalid or the output buffer is NULL.

Since: 1.3

Author: Attila Kovacs

See also: novas_timestamp(); novas_timescale_for_string()

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

◆ novas_set_split_time()

int novas_set_split_time	(	enum novas_timescale	timescale,
		long	ijd,
		double	fjd,
		int	leap,
		double	dut1,
		novas_timespec *restrict	time
	)

Sets an astronomical time to the split Julian Date value, defined in the specified timescale. The split into the integer and fractional parts can be done in any convenient way. The highest precision is reached if the fractional part is ≤ 1 day. In that case, the time may be specified to picosecond accuracy, if needed.

The accuracy of Barycentric Time measures (TDB and TCB) relative to other time measures is limited by the precision of tbd2tt() implementation, to around 10 μs.

REFERENCES:

IAU 1991, RECOMMENDATION III. XXIst General Assembly of the International Astronomical Union. Retrieved 6 June 2019.
IAU 2006 resolution 3, see Recommendation and footnotes, note 3.
Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
Kaplan, G. (2005), US Naval Observatory Circular 179.
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

	timescale	The astronomical time scale in which the Julian Date is given
	ijd	[day] integer part of the Julian day in the specified timescale
	fjd	[day] fractional part Julian day value in the specified timescale
	leap	[s] Leap seconds, e.g. as published by IERS Bulletin C.
	dut1	[s] UT1-UTC time difference, e.g. as published in IERS Bulletin A.
[out]	time	Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns: 0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also: novas_set_time(); novas_set_unix_time(); novas_get_split_time(); novas_timescale_for_string()

Since: 1.1

Author: Attila Kovacs

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, NOVAS_UTC, and tt2tdb().

◆ novas_set_time()

int novas_set_time	(	enum novas_timescale	timescale,
		double	jd,
		int	leap,
		double	dut1,
		novas_timespec *restrict	time
	)

Sets an astronomical time to the fractional Julian Date value, defined in the specified timescale. The time set this way is accurate to a few μs (microseconds) due to the inherent precision of the double-precision argument. For higher precision applications you may use novas_set_split_time() instead, which has an inherent accuracy at the picosecond level.

Parameters

	timescale	The astronomical time scale in which the Julian Date is given
	jd	[day] Julian day value in the specified timescale
	leap	[s] Leap seconds, e.g. as published by IERS Bulletin C.
	dut1	[s] UT1-UTC time difference, e.g. as published in IERS Bulletin A.
[out]	time	Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns: 0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also: novas_set_split_time(); novas_set_unix_time(); novas_get_time(); novas_timescale_for_string()

Since: 1.1

Author: Attila Kovacs

References novas_set_split_time().

◆ novas_set_unix_time()

int novas_set_unix_time	(	time_t	unix_time,
		long	nanos,
		int	leap,
		double	dut1,
		novas_timespec *restrict	time
	)

Sets an astronomical time to a UNIX time value. UNIX time is defined as UTC seconds measured since 0 UTC, 1 Jan 1970 (the start of the UNIX era). Specifying time this way supports precisions to the nanoseconds level by construct. Specifying UNIX time in split seconds and nanoseconds is a common way CLIB handles precision time, e.g. with struct timespec and functions like clock_gettime() (see time.h).

Parameters

	unix_time	[s] UNIX time (UTC) seconds
	nanos	[ns] UTC sub-second component
	leap	[s] Leap seconds, e.g. as published by IERS Bulletin C.
	dut1	[s] UT1-UTC time difference, e.g. as published in IERS Bulletin A.
[out]	time	Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns: 0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also: novas_set_time(); novas_get_unix_time(); clock_gettime(); struct timespec

Since: 1.1

Author: Attila Kovacs

References novas_set_split_time(), and NOVAS_UTC.

◆ novas_timescale_for_string()

enum novas_timescale novas_timescale_for_string ( const char *restrict str )

Returns the timescale constant for a string that denotes the timescale in with a standard abbreviation (case insensitive). The following values are recognised: "UTC", "UT", "UT0", "UT1", "GMT", "TAI", "GPS", "TT", "ET", "TCG", "TCB", "TDB".

Parameters

str	String specifying an astronomical timescale

Returns: The SuperNOVAS timescale constant (<=0), or else -1 if the string was NULL, empty, or could not be matched to a timescale value (errno will be set to EINVAL also).

Since: 1.3

Author: Attila Kovacs

See also: novas_parse_timescale(); novas_set_time(); novas_set_split_time(); novas_print_timescale()

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

◆ novas_timestamp()

int novas_timestamp	(	const novas_timespec *restrict	time,
		enum novas_timescale	scale,
		char *restrict	dst,
		int	maxlen
	)

Prints a timestamp to millisecond precision in the specified timescale to the specified string buffer. E.g.:

 2025-01-26T21:32:49.701 TAI

NOTES:

The timestamp uses the astronomical date. That is Gregorian dates after the Gregorian calendar reform of 15 October 1582, and Julian/Roman dates prior to that.
B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

	time	Pointer to the astronomical time specification data structure.
	scale	The timescale to use.
[out]	dst	Output string buffer. At least 28 bytes are required for a complete timestamp with termination.
	maxlen	The maximum number of characters that can be printed into the output buffer, including the string termination. If the full ISO timestamp is longer than `maxlen`, then it will be truncated to fit in the allotted space, including a termination character.

Returns: the number of characters printed into the string buffer, not including the termination. As such it is at most maxlen - 1.

Since: 1.3

Author: Attila Kovacs

See also: novas_iso_timestamp()

References novas_get_split_time(), and novas_print_timescale().

◆ tdb2tt()

int tdb2tt	(	double	jd_tdb,
		double *restrict	jd_tt,
		double *restrict	secdiff
	)

Computes the Terrestrial Time (TT) or Terrestrial Dynamical Time (TDT) Julian date corresponding to a Barycentric Dynamical Time (TDB) Julian date.

Expression used in this function is a truncated form of a longer and more precise series given in the first reference. The result is good to about 10 microseconds.

Deprecated:: Use the less computationally intensive an more accurate tt2tdb() routine instead.

REFERENCES:

Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
Kaplan, G. (2005), US Naval Observatory Circular 179.
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

	jd_tdb	[day] Barycentric Dynamic Time (TDB) based Julian date
[out]	jd_tt	[day] Terrestrial Time (TT) based Julian date. (It may be NULL if not required)
[out]	secdiff	[s] Difference 'tdb_jd'-'tt_jd', in seconds. (It may be NULL if not required)

Returns: 0 if successful, or -1 if the tt_jd pointer argument is NULL.

See also: tt2tdb()

◆ tt2tdb()

double tt2tdb ( double jd_tt )

Returns the TDB - TT time difference in seconds for a given TT date.

Note, as of version 1.1, it uses the same calculation as the more precise original tdb2tt(). It thus has an acuracy of about 10 μs vs around 30 μs with the simpler formula from the references below.

REFERENCES

Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
Kaplan, G. (2005), US Naval Observatory Circular 179.
https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

jd_tt [day] Terrestrial Time (TT) based Julian date

Returns: [s] TDB - TT time difference.

See also: tdb2tt()

Since: 1.0

Author: Attila Kovacs

References tdb2tt().

Macros

Functions

Detailed Description

Function Documentation

◆ get_ut1_to_tt()

◆ get_utc_to_tt()

◆ novas_date()

◆ novas_date_scale()

◆ novas_diff_tcb()

◆ novas_diff_tcg()

◆ novas_diff_time()

◆ novas_get_split_time()

◆ novas_get_time()

◆ novas_get_unix_time()

◆ novas_iso_timestamp()

◆ novas_offset_time()

◆ novas_parse_date()

◆ novas_parse_date_format()

◆ novas_parse_timescale()

◆ novas_print_timescale()

◆ novas_set_split_time()

◆ novas_set_time()

◆ novas_set_unix_time()

◆ novas_timescale_for_string()

◆ novas_timestamp()

◆ tdb2tt()

◆ tt2tdb()